1. Field of the Invention
The present invention relates to an apparatus for growing a semiconductor single crystal according to the Czochralski method, and a method of growing the same. More, particularly, the present invention relates to an apparatus for and a method of growing a crystal by rotating a semiconductor melt.
2. Description of the Related Art
Single crystal wafers of semiconductor used for substrates of ultra-high density electronic devices are made by growing the crystal according to the Czochralski method wherein the semiconductor single crystal is pulled up from a rotating semiconductor melt while rotating the single crystal in the direction opposite to that of the melt. The semiconductor melt held in a crucible is supplied with heat from a cylindrical heater disposed around the crucible. The crucible is rotated so as to make the temperatures in the melt due to the heat distributed in an axially symmetric configuration with respect to the pull shaft of the crystal. In order to make the temperature distribution in the melt axially symmetric sufficiently, the center of the crucible rotation and the center of the heater must correspond to the pull shaft of the crystal.
In the prior art, mechanical means has been predominantly employed for rotating the shaft which holds the crucible in the heater. Also, a method of supplying a current of different phase to a heater so that the semiconductor melt rotates spontaneously due to the rotating magnetic field generated thereby is disclosed in Japanese Journal of Applied Physics, vol.19 (1980), L33-36. Also, Japanese Patent Kokai Publication No. 63-60189 discloses a method of disposing several electromagnet coils around a crystal growing furnace so that the semiconductor melt rotates spontaneously due to the rotating magnetic field generated by changing the phase of the current supplied to the electromagnet coil.
However, these methods of rotating the semiconductor melt of the prior art have such problems as described below.
With the method of mechanically rotating the crucible holding shaft, when the semiconductor crystal to be grown is made as large as 30 cm in diameter, it is necessary to use 300 kg or more semiconductor melt, which leads to an inconveniently large apparatus. As the apparatus becomes larger, it becomes more difficult to rotate the crucible at a constant speed without the rotation shaft deviating from the center.
With the method of supplying alternating current to the heater, the heater temperature changes due to the alternating current which in turn causes variations in the semiconductor melt temperature. Also this method gives rise to such problems as the deformation of the heater due to the alternating current thus making it necessary to reinforce the heater in the case of large single crystal of semiconductor, and is not suited for growing single crystal of a large diameter.
The method of generating a rotating magnetic field by means of the electromagnet coils requires it to control the phase of the current supplied to the coils in order to achieve constant rotation of the magnetic field and to control the positional relationship of the coils accurately, and moreover it is difficult to control the rotation rate to a desired value.
Thus when a semiconductor single crystal having a large diameter of 30 cm or greater is to be grown with the prior art technologies, temperature distribution in the interface of crystal growth becomes asymmetrical with respect to the pull shaft unless the rotation axis of the semiconductor melt corresponds completely with the pull shaft, leading to asymmetric distribution of temperatures in the interface of crystal growth and uneven distribution of impurities in the single crystal which has been grown resulting in striation.